A turbine engine has a compressor section, a combustor section and a turbine section. In operation, the compressor section can induct ambient air and compress it. The compressed air can enter the combustor section and can be distributed to each of the combustors therein. FIG. 1 shows one example of a known combustor 10. The combustor 10 can include a pilot swirler 12 (or more generally, a pilot burner). A plurality of main swirlers 14 can be arranged circumferentially about the pilot swirler 12. Fuel is supplied to the pilot swirler 12 and separately to the plurality of main swirlers 14 by fuel supply nozzles (not shown). When the compressed air 16 enters the combustor 10, it is mixed with fuel in the pilot swirler 12 as well as in the surrounding main swirlers 14. Combustion of the air-fuel mixture occurs downstream of the swirlers 12, 14 in a combustion zone 20, which can be largely enclosed within a combustor liner 22. As a result, a hot working gas is formed. The hot working gas can be routed to the turbine section, where the gas can expand and generate power that can drive a rotor.
During engine operation, acoustic pressure oscillations at undesirable frequencies can develop in the combustor section due to, for example, burning rate fluctuations inside the combustor section. Such pressure oscillations can damage components in the combustor section. To avoid such damage, one or more damping devices can be associated with the combustor section of a turbine engine. One commonly used damping device is a resonator 24, which can be a Helmholtz resonator. Various examples of Helmholtz resonators are disclosed in U.S. Pat. Nos. 6,530,221 and 7,080,514. Generally, a resonator 24 can be formed by attaching a resonator box 26 to a surface of a combustor section component, such as an outer peripheral surface 28 of the combustor liner 22. A plurality of resonators 24 can be aligned circumferentially about the liner 22.
Each resonator 24 can be tuned to provide damping at a desired frequency or across a range of frequencies. While many efforts in resonator design have been directed to optimizing the acoustic damping performance of resonators, there is still an ongoing need for a more effective and efficient resonator system.
In addition to acoustic damping, the resonators 24 can serve an important cooling function. A resonator plate 30 of the resonator box 26 can include a plurality of holes 32 through which air can enter and purge an internal cavity formed between the resonator box 26 and the liner 22. One beneficial byproduct of such airflow is that the air can pass through the holes 32 and directly impinge on the hot surface of the liner 22, thereby providing impingement cooling to the liner 22.
Further, the liner 22 can be perforated with holes 38. Each resonator box 26 is welded to the liner 22 around a group 39 of the holes 38. Thus, air entering the resonator 24 through the holes 32 in the resonator box 26 can exit the resonator 24 by flowing through the holes 38 in the liner 22. Such flow can provide a film cooling effect on the inner peripheral surface 40 of the liner 22.
However, there can be wide variation in the temperature distribution of the fluid flow 23, including the combustion flame, within the liner 22, which is due to the arrangement of the main swirlers 14. Specifically, the fluid flow 23 exhibits a pattern of alternating relatively hot temperature regions and relatively cold temperature regions in the circumferential direction, particularly at or near the inner peripheral surface 40 of the liner 22. For each main swirler 14, there is a corresponding hot region in the fluid flow. Each hot region may be generally aligned with a corresponding one of the main swirlers 14, but they can be offset due to the swirl angle. In between each pair of neighboring hot regions, the flame is relatively cold, thereby forming a cold region in the fluid flow. The difference in temperature between the hot and cold regions of the fluid flow 23 at or near the inner peripheral surface 40 of the liner 22 can be at least about 100 degrees Celsius. As the flame progresses downstream, the hot and cold regions of the fluid flow 23 can merge so that there is less of a temperature difference between the hot and cold regions in the fluid flow 23.
The liner 22 itself has alternating hot and cold regions in the circumferential direction generally corresponding to the temperature distribution of the fluid flow within the liner 22. The difference in temperature between the hot and cold regions of the liner 22 can be generally the same as the difference in temperature between the hot and cold regions of the fluid flow at or near the inner peripheral surface 40 of the liner 22. However, the difference in liner temperature between the hot and cold regions can be affected by a number of additional factors.
The placement of resonators based chiefly on acoustic considerations can lead to non-optimized cooling and possibly an increase in undesired emissions. For instance, if a resonator with a relatively high rate of airflow therethrough is provided in a cold region of the liner, then this portion of the liner is being overly cooled. The excess amount of cooling air results in higher combustion emissions of oxides of nitrogen (NOx). Instead of being wasted, such cooling air could be put to beneficial uses elsewhere in the engine. Likewise, if a resonator with a relatively low rate of airflow therethrough is provided in a hot region of the liner, then this portion of the liner may not be adequately cooled, potentially degrading the integrity of the liner.
Thus, there is a need for a resonator system that can improve the cooling effectiveness of the resonators and/or improve the acoustic performance of the resonators.